A horizontal axis wind turbine consists of a stationary tower that elevates a nacelle bearing an electrical generator attached to a rotor mechanically. The rotor comprises a hub that attaches at least one blade, which transforms the wind's kinetic energy in the rotating rotor.
It is known in the state of the art that the optimum operating point of a horizontal axis wind turbine is achieved when the rotor shaft is parallel to the direction of the wind, since this maximizes the energy produced while minimizing loads. However, the optimum production and the maximum perpendicularity to the wind do not coincide in general, due to any wind condition that generates speed asymmetries in the rotor plane. This is wind dependent and different in each wind turbine.
The nacelle is capable of moving on its supporting tower to enable the rotor to position itself (yawing) in the direction of the wind through a mechanical system that moves it to the desired orientation (yaw system) with a view to best harnessing the wind and producing the most power. This yaw system turns the wind turbine nacelle around a vertical yaw axis, which coincides with the vertical axis of the tower until the rotational axis of the blades are parallel with the wind direction. When this optimum position is not reached, the wind turbine has a yaw error determined by the angle of deviation with respect to said optimal position.
However, given the natural variability of the wind direction, there is a need for systems that constantly detect the wind direction and consequently adjust the position of the wind turbine so as to best harness the wind to produce maximum power. However, extreme misalignment with respect to the wind direction also causes an increase in loads on wind turbine components, resulting in the deterioration thereof.
In this regard, the yaw system has a wind direction measuring system comprising sensors, usually installed at the top of the wind turbine nacelle behind the rotor.
Nonetheless, in wind direction measurement there are various factors to consider that could cause retrieval of a flawed measurement value, namely the rotor's influence on the descending air currents, faulty operation of the sensors because of erroneous installation and/or configuration, ascending airflow due to the location of each wind turbine and, lastly, developments in internal blade section designs, which have evolved toward greater aerodynamic effectiveness and produce greater airflow deflection. The foregoing causes the wind turbine not to operate in the desired conditions.
US2015086357A1 describes a method for adjusting yaw bias in wind turbine defining an operational condition for the wind turbine during operation of the wind turbine. This method is hardly automatable, requiring subsequent manual procedures.
There are solutions in the state of the art that address misalignment issues by positioning the sensors in front of the wind turbine rotor, e.g., patent EP2626549A1.
Patent US2013114067A1 describes an optical control system for a wind turbine comprising the incorporation of some sensors at the front of the wind turbine rotor that provides some measurements that, in combination with the data obtained in the wind turbine nacelle sensors, enable the positioning of the wind turbine in the optimum position.
Known state of the art includes other solutions such as patent EP2267301B1, which describes a wind turbine yaw control system that incorporates a wind channel that runs through the wind turbine hub and comprises an air flow measuring device to determine the yaw error through a control system. However, this solution cannot be applied to wind turbines that are already installed.
The existing solutions in the state of the art are based on the same idea: to measure the wind in the rotor and its comparison with the measurement of the sensor in the nacelle. This requires the use of additional sensors to those existing in a wind turbine (speed measurement sensors, wind direction measurement, power measurement and rotor rotation measurement) with the cost involved, in addition to the installation, removal and calibration of each measuring device of each wind turbine that needs to be adjusted.
In light of the drawbacks of the aforementioned solutions, a need is thus envisioned for implementing a solution that could, by employing the means already existing on the wind turbines, guarantee a correct yaw error measurement to be able to position the nacelle wind turbine at the optimum operating position to assure the efficiency. The characteristics of the optimization algorithm allow the complete automation of the process, which is a technical advantage over many manual procedures of the state of the art.